Lithium-containing phosphates, method of preparation, and uses thereof

ABSTRACT

The invention provides an electrochemical cell which comprises a first electrode and a second electrode which is a counter electrode to said first electrode. The first electrode comprises a phosphorous compound of the nominal general formula Li 3 E′ a E″ b (PO 4 ) 3 , desirably at least one E is a metal; and preferably, Li 3 M′M″(PO 4 ) 3 . E′ and E″ are the same or different from one another. Where E′ and E″ are the same, they are preferably metals having more than one oxidation state. Where E′ and E″ are different from one another, they are preferably selected from the group of metals where at least one of E′ and E″ has more than one oxidation state.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.08/717,979, filed Sep. 23, 1996, and PCT/US97/15544, filed Sep. 4, 1997,both pending.

FIELD OF THE INVENTION

[0002] This invention relates to improved materials usable as electrodeactive materials, method for making such improved materials, andelectrodes formed from it for electrochemical cells in batteries.

BACKGROUND OF THE INVENTION

[0003] Lithium batteries are prepared from one or more lithiumelectrochemical cells containing electrochemically active(electroactive) materials. Such cells typically include an anode(negative electrode), a cathode (positive electrode), and an electrolyteinterposed between spaced apart positive and negative electrodes.Batteries with anodes of metallic lithium and containing metalchalcogenide cathode active material are known. The electrolytetypically comprises a salt of lithium dissolved in one or more solvents,typically nonaqueous (aprotic) organic solvents. Other electrolytes aresolid electrolytes typically called polymeric matrixes that contain anionic conductive medium, typically a metallic powder or salt, incombination with a polymer that itself may be ionically conductive whichis electrically insulating. By convention, during discharge of the cell,the negative electrode of the cell is defined as the anode. Cells havinga metallic lithium anode and metal chalcogenide cathode are charged inan initial condition. During discharge, lithium ions from the metallicanode pass through the liquid electrolyte to the electrochemical active(electroactive) material of the cathode whereupon they releaseelectrical energy to an external circuit.

[0004] It has recently been suggested to replace the lithium metal anodewith an intercalation anode, such as a lithium metal chalcogenide orlithium metal oxide. Carbon anodes, such as coke and graphite, are alsointercalation materials. Such negative electrodes are used withlithium-containing intercalation cathodes, in order to form anelectroactive couple in a cell. Such cells, in an initial condition, arenot charged. In order to be used to deliver electrochemical energy, suchcells must be charged in order to transfer lithium to the anode from thelithium-containing cathode. During discharge the lithium is transferredfrom the anode back to the cathode. During a subsequent recharge, thelithium is transferred back to the anode where it reintercalates. Uponsubsequent charge and discharge, the lithium ions (Li⁺) are transportedbetween the electrodes. Such rechargeable batteries, having no freemetallic species are called rechargeable ion batteries or rocking chairbatteries. See U.S. Pat. Nos. 5,418,090; 4,464,447; 4,194,062; and5,130,211.

[0005] Preferred positive electrode active materials include LiCoO₂,LiMn₂O₄, and LiNiO₂. The cobalt compounds are relatively expensive andthe nickel compounds are difficult to synthesize. A relativelyeconomical positive electrode is LiMn₂O₄, for which methods of synthesisare known, and involve reacting generally stoichiometric quantities of alithium-containing compound and a manganese containing compound. Thelithium cobalt oxide (LiCOo₂), the lithium manganese oxide (LiMn₂O₄),and the lithium nickel oxide (LiNiO₂) all have a common disadvantage inthat the charge capacity of a cell comprising such cathodes suffers asignificant loss in capacity. That is, the initial capacity available(amp hours/gram) from LiMn₂O₄, LiNiO₂, and LiCoO₂ is less than thetheoretical capacity because less than 1 atomic unit of lithium engagesin the electrochemical reaction. Such an initial capacity value issignificantly diminished during the first cycle operation and suchcapacity further diminishes on every successive cycle of operation. Thespecific capacity for LiMn₂O₄ is at best 148 milliamp hours per gram. Asdescribed by those skilled in the field, the best that one might hopefor is a reversible capacity of the order of 110 to 120 milliamp hoursper gram. obviously, there is a tremendous difference between thetheoretical capacity (assuming all lithium is extracted from LiMn₂O₄)and the actual capacity when only 0.8 atomic units of lithium areextracted as observed during operation of a cell. For LiNiO₂ and LiCoO₂only about 0.5 atomic units of lithium is reversibly cycled during celloperation. Many attempts have been made to reduce capacity fading, forexample, as described in U.S. Pat. No. 4,828,834 by Nagaura et al.However, the presently known and commonly used, alkali transition metaloxide compounds suffer from relatively low capacity. Therefore, thereremains the difficulty of obtaining a lithium- containing chalcogenideelectrode material having acceptable capacity without disadvantage ofsignificant capacity loss when used in a cell.

SUMMARY OF THE INVENTION

[0006] The invention provides novel lithium-containing phosphatematerials having a high proportion of lithium per formula unit of thematerial. Upon electrochemical interaction, such material deintercalateslithium ions, and is capable of reversibly cycling lithium ions. Theinvention provides a rechargeable lithium battery which comprises anelectrode formed from the novel lithium-containing phosphates,preferably lithium-metal -phosphates. Methods for making the novelphosphates and methods for using such phosphates in electrochemicalcells are also provided. Accordingly, the invention provides arechargeable lithium battery which comprises an electrolyte; a firstelectrode having a compatible active material; and a second electrodecomprising the novel phosphate materials. The novel materials,preferably used as a positive electrode active material, reversiblycycle lithium ions with the compatible negative electrode activematerial. Desirably, the phosphate has a proportion in excess of 2atomic units of lithium per formula unit of the phosphate, and uponelectrochemical interaction the proportion of lithium ions per formulaunit become less. Desirably, the lithium-containing phosphate isrepresented by the nominal general formula Li_(a)E′_(b)E″_(c)(PO₄)₃where in an initial condition “a” is about 3, and during cycling variesas 0≦a≦3; b and c are both greater than 0, and b plus c is about 2. Inone embodiment, elements E′ and E″ are the same. In another embodiment,E′ and E″ are different from one another. At least one of E′ and E″ isan element capable of an oxidation state higher than that initiallypresent in the lithium phosphate compound. Correspondingly, at least oneof E′ and E″ has more than one oxidation state. Both E′ and E″ may havemore than one oxidation state and both may be oxidizable from the stateinitially present in the phosphate compound. Desirably, at least one ofE′ and E″ is a metal or semi-metal. Preferably, at least one of E′ andE″ is a metal. Preferably, the metal phosphate is represented by thenominal general formula Li₃M′_(b)M″_(c)(PO₄)₃, where M′ and M″ are eachmetals, b plus c is about 2, and M′ and M″ satisfy the conditions ofoxidizability and oxidation state given for E′ and E″. Many combinationssatisfying the above conditions are possible. For example, in oneembodiment M′ and M″ are each transition metals. In still anotherembodiment where the formulation Li₃M′M″ (PO₄)₃ comprises two differentmetals, M′ and M″, one metal M′ may be selected from non-transitionmetals and semi-metals. In another embodiment, such nontransition metalhas only one oxidation state and is nonoxidizable from its oxidationstate in the final compound Li₃M′M″(PO₄) ₃. In this case, M′ may beselected from metals, such as aluminum, magnesium, calcium, potassium,and other Groups I and II metals. In this case, M″ is a metal havingmore than one oxidation state, and is oxidizable from its oxidationstate in the end product, and M″ is preferably a transition metal. Inanother embodiment, the non-transition metal has more than one oxidationstate. Examples of semi-metals having more than one oxidation state areselenium and tellurium; other non-transition metals with more than oneoxidation state are tin and lead. Metallic elements include metals andsemi-metals, such as semi-conductors, including silicon (Si), tellurium(Te), selenium (Se), antimony (Sb), and arsenic (As). The metalphosphates are alternatively represented by the nominal general formulaLi_(3−x)M′M″(PO₄)₃ (0≦x≦3), signifying capability to deintercalate andreinsert lithium. Li_(3−x)M′_(y)M″_(2−y)(PO₄)₃ signifies that therelative amount of M′ and M″ may vary, with o<y<2, some M′ and M″ areeach present. The same criteria as to the values of x and y apply toLi_(3−x)E′_(y)E″_(2−y)(PO₄)₃. The active material of the counterelectrode is any material compatible with the lithium-metal-phosphate ofthe invention. Where the lithium-metal-phosphate is used as a positiveelectrode active material, metallic lithium may be used as the negativeelectrode active material where lithium is removed and added to themetallic negative electrode during use of the cell. The negativeelectrode is desirably a nonmetallic intercalation compound. Desirably,the negative electrode comprises an active material from the groupconsisting of metal oxide, particularly transition metal oxide, metalchalcogenide, carbon, graphite, and mixtures thereof. It is preferredthat the anode active material comprises graphite. Thelithium-metal-phosphate of the invention may also be used as a negativeelectrode material.

[0007] The present invention resolves the capacity problem posed bywidely used cathode active material. It has been found that the capacityof cells having the preferred Li₃M′M″(PO₄)₃ active material of theinvention are greatly improved, for example, over LiMn₂O₄. Optimizedcells containing lithium-metal-phosphates of the invention potentiallyhave performance greatly improved over all of the presently used lithiummetal oxide compounds. Advantageously, the novel lithium-metal-phosphatecompounds of the invention are relatively easy to make, and readilyadaptable to commercial production, are relatively low in cost, and havevery good specific capacity.

[0008] Objects, features, and advantages of the invention include animproved electrochemical cell or battery based on lithium which hasimproved charging and discharging characteristics, a large dischargecapacity, and which maintains its integrity during cycling. Anotherobject is to provide a cathode active material which combines theadvantages of large discharge capacity and with relatively lessercapacity fading. It is also an object of the present invention toprovide positive electrodes which can be manufactured more economicallyand relatively more conveniently, rapidly, and safely than presentpositive electrodes which react readily with air and moisture. Anotherobject is to provide a method for forming cathode active material whichlends itself to commercial scale production providing for ease ofpreparing large quantities.

[0009] These and other objects, features, and advantages will becomeapparent from the following description of the preferred embodiments,claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is an EVS (Electrochemical Voltage Spectroscopy)voltage/capacity profile for a cell embodying thelithium-metal-phosphate material of the invention Li₃V₂(PO₄)₃ incombination with a lithium metal counter electrode in an electrolytecomprising ethylene carbonate (EC) and dimethyl carbonate (DMC) in aweight ratio of 2:1 and including a 1 molar concentration of LiPF₆ salt.The lithium-metal-phosphate containing electrode and the lithium metalcounter electrode are maintained spaced apart by a separator of fiberglass which is interpenetrated by the solvent and the salt. Theconditions are ±10 mV steps, between about 3.0 and 4.2 volts, and thecritical limiting current density is less than or equal to 0.05 mA/cm².

[0011]FIG. 2 is an EVS differential capacity plot for the cell asdescribed in connection with FIG. 1.

[0012]FIG. 3 is a voltage/capacity plot of Li₃V₂(PO₄)₃ cycled with alithium metal anode using constant current cycling at ±0.2 milliamps persquare centimeter in a range of 3.0 to 4.3 volts.

[0013]FIG. 4 is a two-part graph based on multiple constant currentcycling of Li₃V₂(PO₄)₃ cycled with a lithium metal anode using theelectrolyte as described in connection with FIG. 1 and cycled, chargeand discharge at ±0.25 milliamps per square centimeter, 3.0 to 4.2volts. In the two-part graph, FIG. 4A shows the excellentrechargeability of the lithium-metal-phosphate/lithium metal cell. FIG.4B shows the excellent cycling and capacity of the cell.

[0014]FIG. 5 is an illustration of a cross section of a thin battery orcell embodying the invention.

[0015]FIG. 6 shows the results of an x-ray diffraction analysis of theLi₃V₂(PO₄)₃ prepared according to the invention using CuKa radiation,λ=1.5418 Å.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention provides lithium-containing phosphatematerials, preferably lithium-metal-phosphates, which are usable aselectrode active materials, for the first time, as a source of lithium(Li⁺) ions. Upon extraction of x lithium ions from the preferredLi_(3−x)M′M″(PO₄)₃, significant capacity is achieved. Such specificcapacity achieved from preferred lithium-metal-phosphates is far inexcess of the specific capacity from Li₁Mn₂O₄ (Li_(1−x)Mn₂O₄) , anexample of a currently used cathode active material. In the method ofthe invention, electrochemical energy is provided by deintercalation oflithium from lithium-metal-phosphates (Li₃M′M″(PO₄)₃). For example, whenlithium is removed per formula unit of the Li₃M′M″(PO₄)₃, vanadium isoxidized from vanadium III to vanadium IV or V in Li₃M₂(PO₄)₃, M₂=V₂.

[0017] When 1 lithium is removed per formula unit of the lithiumvanadium phosphate, V^(III) is oxidized to V^(IV). The electrochemicalreaction is as shown below:

Li ₃ V ⁺³ V ⁺³(PO ₄)₃ →Li ₂ V ⁺³ V ⁺⁴(PO ₄)₃ +Li ⁺ +e ⁻

[0018] Further extraction is possible according to:

Li ₂ V ⁺³ V ⁴ (PO ₄)₃ →Li ₁ V ⁺⁴ V ⁺⁴ (PO ₄)₃ +Li ⁺ +e ⁻

[0019] Note that the average oxidation state of vanadium is +4 (IV). Itis thought that both of the vanadium atomic species carry a +4 charge,it is less likely that one of the vanadium species carries a +3 chargeand the other a +5 charge. Advantageously, still further oxidation ispossible with the removal of the final lithium ion according to theEquation:

Li ₁ V ⁺⁴ V ⁴ (PO ₄)₃ →V ^(′4) V ⁺⁵ (PO ₄)₃ +Li ⁺ +e ⁻

[0020] In the overall equation Li₃V⁺³V⁺³(PO₄)₃→V⁺⁴V⁺⁵(PO₄)₃+3Li⁺+3e⁻,this material has a theoretical capacity of 197 milliamp hours per gramupon electrochemical oxidation as per the reaction shown herein. Theelectrochemical extraction of lithium from Li₃M′M″(PO₄)₃ is heretoforenot known to have been described. Similarly, a mixed metal compound,such as Li₃FeV(PO₄)₃, has two oxidizable elements. In contrast,Li₃AlTm(PO₄)₃ has one oxidizable metal, the transition metal (Tm).

[0021]FIGS. 1 through 4 which will be described more particularly belowshows capacity in actual use where the lithium-metal-phosphate cathode(positive electrode) of the invention was tested in a cell comprising alithium metal counter electrode (negative electrode) and an EC:DMC-LiPF,electrolyte, with operation between about 3.0 and 5.0 volts versus L/Li⁺where lithium is cycled between the positive electrode and the negativeelectrode.

[0022] In another aspect, the invention provides a lithium ion batterywhich comprises an electrolyte; a negative electrode having anintercalation active material; and a positive electrode comprising alithium-metal-phosphate active material characterized by an ability todeintercalate lithium ions for intercalation into the negative electrodeactive material. The lithium-metal-phosphate is desirably represented bythe nominal general formula Li₃M′M″(PO₄)₃. In one aspect, the metals M′and M″ are the same and in another aspect, the metals M′ and M″ aredifferent. Desirably, the phosphate is the compound Li₃M₂(PO₄)₃ where Mis a transition metal, and M is most desirably V, Fe, Sr, and Mn. Thelithium-metal-phosphate is preferably a compound represented by thenominal general formula Li_(3−x)V₂(PO₄)₃, signifying the preferredcomposition and its capability to deintercalate lithium. The presentinvention resolves a capacity problem posed by conventional cathodeactive materials. Such problems with conventional active materials aredescribed by Tarascon in U.S. Pat. No. 5,425,932, using LiMn₂O₄ as anexample. Similar problems are observed with LiCoO₂, LiNiO₂, and many, ifnot all, lithium metal chalcogenide materials. The present inventiondemonstrates that such capacity problems are overcome and greaterproportion of potential in the cathode active material is utilizableproviding a great improvement over conventional active materials.

[0023] The positive electrode active material in an initial condition isrepresented by the molecular formula Li_(3−x)M′M″(PO₄)₃. When used in acell it deintercalates a quantity of x lithium ions for intercalationinto the negative electrode, where the amount of x ions deintercalatedis greater than 0 and less than or equal to 3. Accordingly, duringcycling, charge and discharge, the value of x varies as x greater thanor equal to 0 and less than or equal to 3.

[0024] Positive electrode lithium-metal-phosphate active material wasprepared and tested in electrochemical cells and the results arereported in FIGS. 1 through 4. A typical cell configuration will bedescribed with reference to FIG. 5.

[0025] A description of the electrochemical cell or battery which usesthe novel active material of the invention will now be described. Byconvention, an electrochemical cell comprises a first electrode, acounter electrode which reacts electrochemically with the firstelectrode, and an electrolyte which is capable of transferring ionsbetween the electrodes. A battery refers to one or more electrochemicalcells. Referring to FIG. 5, an electrochemical cell or battery 10 has anegative electrode side 12, a positive electrode side 14, and anelectrolyte/separator 16 therebetween. The negative electrode is theanode during discharge, and the positive electrode is the cathode duringdischarge. The negative electrode side includes current collector 18,typically of nickel, iron, stainless steel, and copper foil, andnegative electrode active material 20. The positive electrode sideincludes current collector 22, typically of aluminum, nickel, andstainless steel, and such foils may have a protective conducting coatingfoil, and a positive electrode active material 24. Theelectrolyte/separator 16 is typically a solid electrolyte, or separatorand liquid electrolyte. Solid electrolytes typically referred to aspolymeric matrixes which contain an ionic conductive medium. Liquidelectrolytes typically comprise a solvent and an alkali metal salt whichform an ionically conducting liquid. In this latter case, the separationbetween the anode and cathode is maintained, for example, by arelatively inert layer of material such as glass fiber. The electrolyteis not an essential feature of the invention. Essentially, any lithiumion containing conducting electrolyte may be used, that is stable up to4.5 volts or more. Essentially any method may be used to maintain thepositive and negative electrodes spaced apart and electrically insulatedfrom one another in the cell. Accordingly, the essential features of thecell are the positive electrode, a negative electrode electricallyinsulated from the positive electrode, and an ionically conductingmedium between the positive and negative electrodes. Examples of asuitable separator/electrolyte, solvents, and salts are described inU.S. Pat. No. 4,830,939 showing a solid matrix containing an ionicallyconducting liquid with an alkali metal salt where the liquid is anaprotic polar solvent; and U.S. Pat. Nos. 4,935,317; 4,990,413;4,792,504; and 5,037,712. Each of the above patents is incorporatedherein by reference in its entirety.

[0026] Electrodes of the invention are made by mixing a binder, theactive material, and carbon powder (particles of carbon). The binderdesirably is a polymer. A paste containing the binder, active material,and carbon, is coated onto a current collector.

[0027] Positive Electrode

[0028] A positive electrode containing the lithium phosphate compound,preferably lithium-metal-phosphate, active material of the invention isprepared by the following method. For the positive electrode, thecontent was as follows: 50 to 90 percent by weight active material(Li₃M′M″(PO₄)₃); 5 to 30 percent carbon black as the electricallyconductive diluent; and 3 to 20 percent binder. The stated ranges arenot critical. The amount of active material may range from 25 to 85weight percent. The formation of each electrode will now be described.The positive electrode was prepared from mixtures oflithiummetal-phosphate (active material) and EPDM (ethylene propylenediene monomer) as the binder, Shawinigan Black® was used as the carbonpowder conductive diluent. The carbon powder conductive diluent is usedto enhance electronic conductivity of the lithium-metal-phosphate.Shawinigan Black®, available from Chevron Chemical Company, San Ramone,Calif., has a BET average surface area of about 70±5 square meters pergram. Other suitable carbon blacks are sold under the designation SuperP™ and Super S™ available from MMM, a subsidiary of Sedema, whichcarbons have BET surface areas of about 65±5 square meters per gram.(MMM has its headquarters in Brussels, Belgium.) Examples of suitablepolymeric binders include EPDM (ethylene propylene diene termonomers),PVDF (polyvinylidene difluoride), ethylene acrylic acid copolymer, EVA(ethylene vinyl acetate copolymer), copolymer mixtures, and the like. Itis desirable to use either PVDF available from Polysciences Corporationwith a molecular weight of 120,000 or EPDM available from ExxonCorporation and sold under the designation EPDM 2504™. EPDM is alsoavailable from The Aldrich Chemical Company. The description of carbonpowders and binders constitute representative examples and the inventionis not limited thereby. For example, other carbon powders are availablefrom Exxon Chemicals, Inc., Chicago, Ill. under the trade name KetjenBlack EC 600 JD® and polyacrylic acid of average molecular weight240,000 is commercially available from BF Goodrich, Cleveland, Ohiounder the name Good-Rite K702™. The positive electrodes of the inventioncomprised mixtures of the lithium-metal-phosphate active material, thebinder (EPDM), and the carbon particles (Shawinigan Black®). These weremixed and blended together with a solvent. Xylene is a suitable solvent.The mixture was then coated onto an aluminum foil current collector toachieve a desired thickness for the final electrode.

[0029] Electrolyte

[0030] The electrolyte used to form the completed cell is preferably acombination of EC/DMC when a carbon counter electrode is used. That is,ethylene carbonate (EC) and dimethyl carbonate (DMC). The ratio ofEC:DMC was about 2:1 by weight. Generally, when a lithium metal anode isused, the choice of an electrolyte is less restricted. It may be theEC:DMC in a ratio of 2:1 by weight or, for example, EC:PC (propylenecarbonate) in 50:50 by weight ratio. In any case, the preferred salt is1 molar LiPF₆. Positive and negative electrodes are maintained in aseparated condition using a fiber glass layer. Such separation can alsobe achieved using a layer of Celgard™. Hoechst—Celanese Corp., Celgard2400™, porous polypropylene, 25 microns thick.

[0031] Negative Electrode

[0032] The electrochemical cell used with the positive electrode andelectrolyte may contain one of a variety of negative electrode activematerials. In one embodiment, the negative electrode may be metalliclithium. In more desirable embodiments, the negative electrode is anintercalation active material, such as, metal oxides and graphite. Whena metal oxide active material is used, the components of the electrodeare the metal oxide, electrically conductive carbon black, and binder inthe proportions as described above for the positive electrode.Representative, but not limiting, examples include coke, graphite, WO₃,Nb₂O₅, and V₆O₁₃. In a preferred embodiment, the negative electrodeactive material is graphite particles. For test purposes, fordetermining capacity of a positive electrode, test cells were fabricatedusing the lithium metal active material. When test cells are formed suchas to be used as batteries, a nonmetallic intercalation graphiteelectrode is preferred. The preferred graphite-based negative electrodecomprises about 80 to 95 percent by weight graphite particles, and morepreferably about 90 percent by weight with the balance constituted by abinder. Preferably, the anode is prepared from a graphite slurry asfollows. A polyvinylidene difluoride (PVDF) solution is prepared bymixing 300 grams of 120,000 MW PVDF (PolyScience) in 300 ml of dimethylformamide. The mixture was stirred for 2 to 3 hours with a magneticstirrer to dissolve all of the PVDF. The PVDF functions as a binder forthe graphite in the anode. Next, a PVDF/graphite slurry is prepared byfirst adding 36 grams of graphite (SFG-15) into about 38.5 grams of thePVDF solution. The mixture is homogenized with a commercial homogenizeror blender. (For example, Tissue Homogenizer System from Cole-ParmerInstrument Co., Niles, Ill.). The viscosity of the slurry is adjusted toabout 200 cp with additional PVDF solution. The slurry is coated onto abare copper foil by standard solvent casting techniques, such as by adoctor blade type coating. (Alternatively, the slurry can be coated ontoa copper foil having a polymeric adhesion promoter layer, describedabove.) In preparing the slurry, it is not necessary to grind or dry thegraphite, nor is it necessary to add conductive carbon black to thegraphite anode formulation. Finally, the electrodes are dried atapproximately 150° C. for 10 hours to remove residual water prior tomaking the electrochemical cells.

[0033] In one embodiment, the negative electrode has thelithium-metal-phosphate compound as the active material. In the case ofLi₃V⁺³V⁺³ (PO₄)₃, the V⁺³ would theoretically be reduced to V⁺². ForLi₃Fe⁺³Fe⁺³ (PO₄)₃, the same activity is theoretically possible, sinceFe⁺² is a stable and common oxidation state for Fe. This should allowtwo more lithium ions to be inserted. That is, Li_(3+x)Fe₂(PO₄) ₃, x isabout 2.

[0034] Various methods for fabricating electrochemical cells and forforming electrode components are described herein. The invention is not,however, limited by any particular fabrication method as the noveltylies in the unique positive electrode material itself and combination ofpositive and negative electrode materials. Accordingly, additionalmethods for preparing electrochemical cells and batteries may beselected and are described in the art, for example, in U.S. Pat. Nos.5,435,054 (Tonder & Shackle); 5,300,373 (Shackle); 5,262,253 (Golovin);4,668,595; and 4,830,939 (Lee & Shackle) . Each of the above patents isincorporated herein by reference in its entirety.

[0035] In one embodiment, the present invention provides a method ofpreparing a compound of the nominal general formula Li₃M′M″(PO₄)₃. Themethod comprises providing a lithium-containing compound, one or moremetal oxide compounds, and a phosphoric acid containing compound.Preferably, the lithium-containing compound is a lithium salt and thephosphoric acid compound is a phosphoric acid salt. The lithiumcompound, one or more metal oxide compounds, and phosphoric acid basedcompound are mixed together in a proportion which provides the statednominal general formula. Such precursor compounds are intimately mixedand then reacted together where the reaction is initiated by heat and ispreferably conducted in a nonoxidizing, reducing atmosphere, whereby thelithium, metal from a metal oxide, and phosphate combine to form theLi₃M′M″(PO₄)₃. Before reacting the compounds, the particles areintermingled to form an essentially homogeneous powder mixture of theprecursors. Such intermingling is preferably conducted by forming a wetmixture using a volatile solvent and then the intermingled particles arepressed together in pellet form in grain-to-grain contact with oneanother. Although it is desired that the precursor compounds be presentin a proportion which provides the stated general formula of theproduct, the lithium compound may be present in an excess amount on theorder of 5 percent excess lithium compared to a stoichiometric mixtureof the precursors. Although a number of lithium compounds are availableas precursors, such as lithium acetate, lithium hydroxide, and lithiumnitrate, lithium carbonate (Li₂CO₃) is preferred for the solid statereaction. The aforesaid precursor compounds are generally crystals,granules, and powders and are generally referred to as being in particleform. Although many types of phosphate salts are known, it is preferredto use ammonium phosphate (NH₄)₂HPO₄. In the case where the compound ofthe formulation Li₃M′M″(PO₄)₃ is desired where M and M′ are the samemetal, a transition metal, such as vanadium, a suitable precursor isvanadium pentoxide (V₂O₅).

[0036] The starting materials are available from a number of sources.The following are typical. Vanadium pentoxide of the general formulaV₂O₅ is obtainable from any number of suppliers including Kerr McGee,Johnson Matthey, or Alpha Products of Davers, Mass. It had a meltingpoint of about 690° C., decomposed at 1750° C., a particle size of lessthan about 60 mesh (250 microns) and had a specific gravity of 3.357grams per cc at 18° C. It was a yellow-red crystalline powder. Vanadiumpentoxide has a CAS number of 1314-62-1. Alternatively, the vanadiumpentoxide may be prepared from ammonium metavanadate (NH₄VO₃). Theammonium metavanadate is heated to a temperature of about 400° C. toabout 450° C. to decompose it to vanadium pentoxide (V₂O₅) . Processesfor production of vanadium pentoxide are described in U.S. Pat. Nos.3,728,442, 4,061,711 and 4,119,707, each of which is incorporated hereinby reference in its entirety.

[0037] In another embodiment, for the formation of Li₃M′M″(PO₄)₃, whereM′ and M″ are different from one another and are metals, preferablytransition metals, one may select two different metal oxide powders,such as titanium oxide (TiO₂), vanadium oxide (V₂O₅), iron oxide (FeO,Fe₂O₃), chromium oxide (CrO₂, CrO, Cr₂O₃), manganese oxide (MnO₂,Mn₃O₄), and the like. In still another embodiment where the formulationLi₃M′M″(PO₄)₃ comprises two different metals, M′ and M″, one metal M′may be selected from non-transition metals and semi-metals. In anotherembodiment, non-transition metal has only one oxidation state and isnonoxidizable from its oxidation state in the final compoundLi₃M′M″(PO₄)₃. In this case, M′ may be selected from metals, such asaluminum and magnesium, calcium, potassium, and other Groups I and IImetals, alkali Group I, and semi-metals. Semi-metals are located in thePeriodic Table on the right hand side and roughly separate the nonmetalsfrom metals, as is well known in the art. In this case, M″ is a metalhaving more than one oxidation state, and is oxidizable from itsoxidation state in the end product, and M″ is preferably a transitionmetal. Examples are Li₃KCr(PO₄)₃ and Li₃KMo(PO₄)₃, where the transitionmetal (Tm) is, respectively, chromium and molybdenum.

Example I

[0038] A preferred procedure for forming the Li₃M′M″(PO₄)₃ compoundactive material will now be described. The method for makingLi₃M′M″(PO₄)₃ will be illustrated by formation of Li₃V₂(PO₄)₃(Li₃M₂(PO₄)₃) . The basic procedure comprised conducting a reactionbetween a lithium compound, preferably lithium carbonate (Li₂CO₃), ametal oxide, preferably vanadium pentoxide (V₂O₅), and a phosphoric acidderivative, preferably the phosphoric acid ammonium acid salt, ammoniumphosphate, NH₄H₂(PO₄) or (NH₄)₂H(PO₄). Each of the precursor startingmaterials are available from a number of chemical outfits includingAldrich Chemical Company and Fluka. The Li₃V₂(PO₄)₃ was prepared withapproximately a stoichiometric mixture of Li₂CO₃, V₂O₅, and (NH₄)₂HPO₄.However, a 5 percent excess of lithium (as lithium carbonate) was usedto minimize any lithium loss as (Li₂O). The precursor materials wereinitially intimately mixed and ground for about 30 minutes in a methanolsolution. The intimately mixed compounds were then dried and pressedinto pellets. Reaction was conducted by heating in an oven at apreferred ramped heating rate of 1° C. per minute up to a temperature ofabout 725° C., and held at 725° C. for about 12 hours to decompose thecarbonate. Then heating continued at the same ramp rate (1° C. perminute) up to a temperature of about 875° C. The mixture was held atthis temperature for about 24 hours. The entire reaction was conductedin a reducing atmosphere under flowing pure hydrogen gas. The flow ratewill depend upon the size of the oven and the quantity needed tomaintain a reducing atmosphere. Based on the size of the oven used inthis example a flow rate of 25 cubic centimeters per minute was used.The oven was permitted to cool down at the end of the 24 hour period,where cooling occurred at a rate of about 3° C. per minute. Then theentire procedure was repeated once again for a further 24 hours. Therepeated steps were also conducted under reducing atmosphere. Althoughhydrogen gas was selected to provide the reducing atmosphere, othermeans for obtaining the reducing atmosphere may be used.

[0039] The general aspects of the above synthesis route are applicableto a variety of starting materials. For example, LiOH and LiNO₃ saltsmay replace Li₂CO₃ as the source of lithium. In this case, thetemperature for the first step will vary due to the differing meltingpoints, 450° C. for LiOH and 700° C. for LiNO₃. The vanadium oxide V₂O₅(V⁺⁵), combined with the oxidizing power of the phosphate anion, isrequired to be offset by a strong reducing agent, for example, thehydrogen atmosphere. Alternatively, lower oxidation state vanadiumcomplexes could be used, e.g., V₂O₃. This is a vanadium in the 3+ state.But because of the presence of PO₄, a certain degree of oxidation mightoccur. Therefore, a reducing agent is used. For example, a mixture of90:10 of Ar:H₂ can be used. The same considerations apply to otherlithium-metal- and phosphate-containing precursors. The relativeoxidizing strength of the selected precursors, and the melting point ofthe salts will cause adjustment in the general procedure, such as,selection of the reducing agent, its reducing capability and flow rate,and the temperature of reaction.

[0040] The final product appeared lime-green in color, and its CuKax-ray diffraction pattern contained all of the peaks expected for thismaterial as shown in FIG. 6. The x-ray diffraction was conducted usingCuKa radiation, λ=1.5418 Å. The pattern evident in FIG. 6 is consistentwith a single oxide compound Li₃V₂(PO₄) 3. This is evidenced by theposition of the peaks in terms of the scattering angle 2 θ (theta), xaxis. The x-ray pattern showed no peaks due to the presence of precursoroxides indicating that the solid state reaction is essentially entirelycompleted. Chemical analysis for lithium and vanadium by atomicabsorption spectroscopy showed, on a percent by weight basis, 5.17percent lithium and 26 percent vanadium. This is close to the expectedresult of 5.11 percent lithium and 25 percent vanadium.

[0041] The chemical analysis and x-ray pattern demonstrate that theproduct of the invention was indeed the nominal general formulaLi₃V₂(PO₄)₃ corresponding to the more generic nominal general formulaLi₃M′M″(PO₄)₃. The term “nominal general formula” refers to the factthat the relative proportion of atomic species may vary slightly on theorder of 2 percent to 5 percent, or more typically, 1 percent to 3percent.

Example II

[0042] The Li₃V₂(PO₄)₃, prepared as described immediately above, wastested in an electrochemical cell. The positive electrode was preparedas described above under the section designated “Positive Electrode”.The negative electrode was metallic lithium. The electrolyte was a 2:1weight ratio mixture of ethylene carbonate and dimethyl carbonate withinwhich was dissolved 1 molar LiPF₆. The cell was cycled between about 3.0and about 4.3 volts with performance as shown in FIGS. 1, 2, 3, 4A, and4B.

[0043]FIG. 1 shows a voltage profile of the test cell, based on theLi₃M′M″(PO₄)₃ positive electrode active material of the invention, andusing a lithium metal counter electrode as described in the examples.The data shown in FIG. 1 is based on the Electrochemical VoltageSpectroscopy (EVS) technique. Electrochemical and kinetic data wererecorded using the Electrochemical Voltage Spectroscopy (EVS) technique.Such technique is known in the art as described by J. Barker in Synth,Met 28, D217 (1989); Synth. Met. 32, 43 (1989); J. Power Sources, 52,185 (1994); and Electrochemica Acta, Vol. 40, No. 11, at 1603 (1995).FIG. 1 clearly shows and highlights the very high and unexpected degreeof reversibility of the lithium ion reactions of the Li₃M′M″(PO₄)3 ₁specifically Li₃V₂(PO₄)₃, active material of the invention. The positiveelectrode contained about 16.8 milligrams of the Li₃M′M″(PO₄)₃ activematerial. The total electrode weight including the binder and conductivecarbon diluent was about 31.2 milligrams. The positive electrode showeda performance of about 136 milliamp hours per gram on the firstdischarge. In FIG. 1, the capacity in is essentially 136 milliamp hoursper gram, and the capacity out is essentially 131 milliamp hours pergram, resulting in essentially no capacity change. FIG. 2 is an EVSdifferential capacity plot based on FIG. 1. As can be seen from FIG. 2,the relatively symmetrical nature of peaks indicates good electricalreversibility, there are small peak separations (charge/discharge), andgood correspondence between peaks above and below the zero axis. Thereare essentially no peaks that can be related to irreversible reactions,since all peaks above the axis (cell charge) have corresponding peaksbelow the axis (cell discharge), and there is essentially no separationbetween the peaks above and below the axis.

[0044]FIG. 3 shows the results of the first constant current cycling at0.20 milliamps per square centimeter between about 3.0 and 4.3 voltsbased upon about 16.8 milligrams of the Li₃V₂(PO₄)₃ active material inthe cathode (positive electrode). In an as prepared, as assembled,initial condition, the positive electrode active material isLi₃V₂(PO₄)₃. The lithium is deintercalated from the Li₃V₂(PO₄)₃ duringcharging of the cell. When fully charged, about 2 units of lithium havebeen removed per formula unit of the originallithium-vanadium-phosphate. Consequently, the positive electrode activematerial corresponds to Li_(3−x)V₂(PO₄)₃ where x is greater than 0 andless than 3, and in the operation of this cell, x appears to be equal toabout 2, when the cathode material is at 4.2 volts versus Li/Li⁺. Inthis charged condition, the electrochemical potential versus lithium ofthe Li₁V₂(PO₄)₃ is about 4.2 volts. The deintercalation of 2 lithiumfrom Li₃V₂ (PO₄)₃ resulting in the Li₁V₂(PO₄)₃, represents approximately127 milliamp hours per gram corresponding to about 2.2 milliamp hoursbased on 16.8 milligrams active material. Next, the cell is dischargedwhereupon a quantity of lithium is reintercalated into the Li₁V₂(PO₄)₃.The average voltage is approximately 3.8 volts versus Li/Li⁺. Thereintercalation corresponds to approximately 101 milliamp hours per gramproportional to the intercalation of about 1.54 atomic units of lithium.The bottom of the curve corresponds to approximately 3.0 volts.

[0045]FIG. 4 presents data obtained by multiple constant current cyclingat 0.25 milliamp hours per square centimeter of the Li₃V₂(PO₄)₃ versuslithium metal counter electrode between 3.0 and 4.2 volts using theelectrolyte and with electrodes formed as described earlier and with aninitial specific capacity of 115 milliamp hours per gram. FIG. 4 is atwo part graph with FIG. 4A showing the excellent rechargeability of theLi/Li₃V₂(PO₄)₃ cell. FIG. 4B shows good cycling and capacity of thecell. The performance shown after 113 cycles is good and shows thatelectrode formulations of the type Li₃M′M″(PO₄)₃ are very desirable.

[0046] It should be noted that the formulations obtained by the methodof the invention demonstrated capacity less than the achievabletheoretical capacity. This is because the method of preparation and cellconfigurations have not yet been optimized for this remarkable material.Nevertheless, this material is highly desirable as an active material toreplace the widely used LiMn₂O₄, Li₁CoO₂, and LiNiO₂, as can be seen byconsidering its theoretical capacity. The theoretical specific capacityfor Li₃V₂(PO₄)₃ is about 190 milliamp hours per gram. This is based onextracting all 3 lithium from the original starting material. Actually,the theoretical capacity is closer to about 197 milliamp hours per gramcorresponding to about 66 milliamp hours for each atomic unit of lithiumextracted from the Li₃V₂(PO₄)₃ compound. Assuming that each suchextracted unit of lithium corresponds to 66 milliamp hours, it can beseen that in FIG. 1 the charge extracted of 136 milliamp hours per gramcorresponds to the extraction of slightly more than 2 units of lithiumfrom the Li₂V₂(PO₄)₃. It should be noted that chemical deintercalationof potassium does not occur from potassium metal phosphates. Heretoforethere has been no attempt to deintercalate lithium from alithium-containing metal phosphate. Thus, the electrochemical reactiondemonstrated by the present invention is remarkable as it has notheretofore been suggested. The product of the present invention may becompared to a Nasicon (Na₃Zr₂PSi₂O₁₂) framework which is a skeletonstructure with an interconnected interstitial space. There are also theLangbeinite-type (K₂Mg₂(SO₄)₃) structures which are true cagestructures. Such structures do not permit mobility of mobile metal ionsthrough the crystal. Some Nasicon-type structures possess ionicconductivity but have very poor electronic conductivity. SomeNasicon-type structures are usable as solid electrolytes, but are notusable as electrode materials. Such Nasicon structures do not have anoxidizable metal in their structure, therefore, an ion cannot beextracted. Thus, such structures and compounds are useless for ionbattery, rocking chair battery, application. In contrast to the knownart, the present invention provides a lithium-metal-phosphate compoundhaving an oxidizable metal. Such metal is capable of more than oneoxidation state. The metal is present in the lithium-metal-phosphatecompound at less than its highest oxidation state. Therefore, the metalis oxidizable to provide capability to extract out one or more Li⁺ ions.This is demonstrated by oxidation of V in Li₃V₂(PO₄)₃ from V⁺³V⁺³ toV⁺⁴V⁺⁵. It should be noted that based on formation of LiVV(PO₄)₃ andLiVFe(PO₄)₃ 1 there are other combinations which make possibleextraction/insertion of Li in such lithium-phosphate compounds. Theoxidation states for such combinations are derived based on theteachings herein and the examples. Note that the amount of Li⁺ removedor added will determine the relative oxidation state of E′ and E″ or M′and M″. Fe in Li₃Fe₂(PO₄)₃ from Fe⁺³Fe⁺³ to Fe⁺⁴Fe⁺⁵ or to Fe⁺⁴Fe⁺⁴; Mnin Li₃Mn₂(PO₄)₃ from Mn⁺³Mn⁺³ to Mn⁴Mn⁴; and other Li₃M₁M₂(PO₄)₃ as perFe⁺³Ti⁺³ to Fe⁺²Ti⁺³ or to Fe⁺³Ti⁺⁴; Co⁺³Mn⁺³ to Co⁺²Mn⁺² or toCo⁺³Mn⁺⁴; Cu⁺³Mn⁺³ to Cu⁺²Mn⁺² or to Cu⁺³Mn⁺⁴, and Fe⁺³V⁺³ to Fe⁺⁴V⁺⁵.

[0047] Lithium ion batteries with this technology are able to be made inthe discharged (pre-charge) state and need a conditioning charge beforeuse. In the initial condition (pre-charge state), anodes of lithium ionbatteries are essentially free of lithium, and often free of ionsthereof, as in the case of graphite. Therefore, such batteries areinherently more stable and relatively less reactive than batteriescontaining LiMn₂O₄ or lithium metal.

[0048] To achieve a useable potential difference, the (positiveelectrode) is electrochemically oxidized, while the anode (negativeelectrode) is reduced. Thus, during charging, a quantity (x) of lithiumions (Li⁺) leave the positive electrode, Li_(3−x)M′_(y)M″_(2−y)(PO₄)₃,and the positive electrode is oxidized, increasing its potential; duringcharging, the Li ions are accepted at or intercalated into a negativeelectrode, preferably a carbon-based negative electrode, which isreduced. As a result, the negative electrode has a potential very closeto the lithium metal potential, which is zero volts. A typical graphiteelectrode can intercalate up to about 1 atom of lithium per each of 6carbons, that is, Li₀C₆ to Li₁C₆. During discharging, the reverseoccurs, and a quantity of (x) of lithium (Li⁺) ions leave the negativeelectrode, increasing its potential. During discharge, the lithium ionsare accepted (intercalated) back into the positive electrode, which isreduced, and its potential is reduced. If the Li₃M′_(y)M″_(2−y)(PO₄)₃compound were used as a negative electrode, during charge, Li ions wouldbe transferred to the negative electrode, as Li_(3+x)M_(y)M_(2−y)(PO₄)₃and the M′, M″, or both, would theoretically achieve a higher oxidationstate. On discharge, the Li⁺ ions would be transferred back to thepositive electrode.

[0049] While this invention has been described in terms of certainembodiments thereof, it is not intended that it be limited to the abovedescription, but rather only to the extent set forth in the followingclaims.

[0050] The embodiments of the invention in which an exclusive propertyor privilege is claimed are defined in the following claims.

What is claimed is:
 1. An electrode having an active material comprisinga lithium-metal-phosphate compound, in an as prepared first condition ofthe nominal general formula Li_((3−x))Fe_(y)E_(2−y)(PO₄)₃, x=0, 0≦y≦2,and E is the same or different from Fe (iron); and characterized by asecond condition of the nominal general formulaLi_((3−x))Fe_(y)E_(2−y)(PO₄)₃, 0<x≦3; where at least one of Fe and E hasan oxidation state higher than its oxidation state in said firstcondition lithium-metal-phosphate compound.
 2. The electrode accordingto claim 1 where E is Fe.
 3. The electrode according to claim 1 where Feand E are different from one another and E is a metal.
 4. The electrodeaccording to claim 1 where Fe and E are different from one another and Eis a transition metal.
 5. The electrode according to claim 1 where Feand E are different from one another, E is an element which is not atransition metal element.
 6. The electrode according to claim 1 whereinsaid E is selected from the group consisting of magnesium (Mg), calcium(Ca), copper (Cu), cobalt (Co), iron (Fe), nickel (Ni), molybdenum (Mo),vanadium (V), chromium (Cr), manganese (Mn), titanium (Ti), and aluminum(Al).
 7. The electrode according to claim 1 wherein saidlithium-metal-phosphate compound is selected from the group consistingof Li₃Fe₂(PO₄)₃, Li₃Fe_(y)V_(2−y)(PO₄)₃, Li₃Fe_(y)Cr_(2−y)(PO₄)₃,Li₃Fe_(y)Mo_(2−y)(PO₄)₃, Li₃Fe_(y)Ni_(2−y)(PO₄ )₃,Li₃Fe_(y)Mn_(2−y)(PO₄)₃, Li₃Fe_(y)Al_(2−y)(PO₄)₃,Li₃Fe_(y)Co_(2−y)(PO₄)₃, and mixtures thereof.
 8. A lithium ionelectrochemical cell which comprises a first electrode, and a secondelectrode which is a counter electrode to said first electrode, saidfirst electrode comprising a lithium-metal-phosphate compound of thenominal general formula Li₃M′_(y)M″_(2−y)(PO₄)₃ where 0≦y≦2, M′ and M″are each metallic elements selected from the group consisting of metaland semi-metal elements, and said M′ and M″ are the same or differentfrom one another: a. where M′ and M″ are the same, they are iron; and b.where M′ and M″ are different from one another, at least one of M′ andM″ is iron.
 9. The cell according to claim 8 wherein M′ and M″ aredifferent from one another and they are transition metals.
 10. The cellaccording to claim 8 wherein M′ and M″ are different from one another,M′ is a metallic element which is not a transition metal, and M″ isiron.
 11. The cell according to claim 8 wherein said Li₃M′M″(PO₄)₃ isselected from the group consisting of Li₃Fe₂(PO₄)₃,Li₃Fe_(y)V_(2−y)(PO₄)₃, Li₃Fe_(y)Cr_(2−y)(PO₄)₃,Li₃Fe_(y)Mo_(2−y)(PO₄)₃, Li₃Fe_(y)Ni_(2−y)(PO₄)₃,Li₃Fe_(y)Mn_(2−y)(PO₄)₃, Li₃Fe_(y)Al_(2−y) (PO₄)₃, Li₃Fe_(y)Co_(2−y)(PO₄)₃, and mixtures thereof.
 12. An electrochemical cell whichcomprises a first electrode and a second electrode which is a counterelectrode to said first electrode, said first electrode comprising alithium-metal-phosphate compound of the nominal general formulaLi₃E′_(y)E″_(2−y)(PO₄)₃ where 0≦y≦2, and elements E′ and E″ are the sameor different from one another: a. where E′ and E″ are the same element,said element is iron; and b. where E′ and E″ are different from oneanother, one is iron.
 13. The cell according to claim 12 wherein atleast one of said E′ and E″ is selected from the group of metal andsemi-metal elements.
 14. An electrode having an active material and abinder, said active material represented by the nominal general formulaLi₃E′_(y)E″_(2−y)(PO₄)₃ wherein said E′ is a transition metal selectedfrom the group consisting of titanium (Ti), vanadium (V), chromium (Cr),manganese (Mn), cobalt (Co), molybdenum (Mo), nickel (Ni), iron (Fe),copper (Cu) and mixtures thereof; said E″ is the same as or differentfrom E′, and E″ is a metal or semi-metal; and 0≦y≦2.
 15. The electrodeof claim 14 wherein E″ is selected from the group consisting ofmagnesium (Mg), calcium (Ca), copper (Cu), cobalt (Co), iron (Fe),nickel (Ni), molybdenum (Mo), aluminum (Al), vanadium (V), chromium(Cr), titanium (Ti), and manganese (Mn).
 16. The electrode of claim 14having said active material where E′ is selected from the groupconsisting of iron and titanium and E″ is a metal or semi-metal.
 17. Theelectrode of claim 14 where E′ and E″ are the same or different from oneanother and are each independently selected from the group consisting ofvanadium (V), chromium (Cr), iron (Fe), titanium (Ti), manganese (Mn),cobalt (Co), molybdenum (Mo), nickel (Ni), alumiunum (Al), copper (Cu),and mixtures thereof.
 18. The electrode of claim 14 wherein said activematerial is represented by Li_(3−x)E′_(y)E″_(2−y)(PO₄)₃, where 3−xsignifies said active material capable of releasing x quantity oflithium, 0≦x≦3.
 19. An electrode having an active material and a binder,said active material represented by the nominal general formulaLi₃E′_(y)E″_(2−y)(PO₄)₃, wherein said E′ is selected from the groupconsisting of Fe and Ti, E″ is different from said selected E′, E″ is ametal or semi-metal, and 0≦y≦2.
 20. The electrode of claim 19 wherein E″is selected from the group consisting of titanium (Ti), magnesium (Mg),calcium (Ca), copper (Cu), cobalt (Co), iron (Fe), nickel (Ni),molybdenum (Mo), aluminum (Al), vanadium (V), chromium (Cr), titanium(Ti), and manganese (Mn).
 21. The electrode of claim 19 wherein saidactive material is represented by Li_(3−x)E′_(y)E″_(2−y)(PO₄)₃, where3−x signifies said active material capable of releasing x quantity oflithium, 0≦x≦3.
 22. An electrode having an active material comprising alithium-metal-phosphate compound, in an as prepared first condition ofthe nominal general formula Li_((3−x))Ti_(y)E_(2−y)(PO₄)₃, X=0, 0≦y≦2,and E is the same or different from Ti (titanium); and characterized bya second condition of the nominal general formulaLi_((3−x))Ti_(y)E_(2−y)(PO₄)₃, 0<x≦3; where at least one of Ti and E hasan oxidation state higher than its oxidation state in said firstcondition lithium-metal-phosphate compound.
 23. The electrode accordingto claim 22 where E is Ti.
 24. The electrode according to claim 22 whereTi and E are different from one another and E is a metal.
 25. Theelectrode according to claim 22 where Ti and E are different from oneanother and E is a transition metal.
 26. The electrode according toclaim 22 where Ti and E are different from one another, E is an elementwhich is not a transition metal element.
 27. The electrode according toclaim 22 wherein said E is selected from the group consisting ofmagnesium (Mg), calcium (Ca), copper (Cu), cobalt (Co), iron (Fe),nickel (Ni), molybdenum (Mo), vanadium (V), chromium (Cr), manganese(Mn), aluminum (Al), and titanium (Ti).
 28. The electrode according toclaim 22 wherein said lithium-metal-phosphate compound is selected fromthe group consisting of Li₃Ti₂(PO₄)₃, Li₃Ti_(y)V_(2−y)(PO₄)₃,Li₃Ti_(y)Fe_(2−y) (PO₄)₃, Li₃Ti_(y)Cr_(2−y)(PO₄)₃,Li₃Ti_(y)Mn_(2−y)(PO₄)₃, Li₃Ti_(y)Mo_(2−y)(PO₄)₃, Li₃Ti_(y)CO_(2−y (PO)₄)₃, Li₃Ti_(y)Al₂(PO₄)₃, Li₃Ti_(y)Ni_(2−y)(PO₄)₃, and mixtures thereof.29. A lithium ion electrochemical cell which comprises a firstelectrode, and a second electrode which is a counter electrode to saidfirst electrode, said first electrode comprising alithium-metal-phosphate compound of the nominal general formulaLi₃M′_(y)M″_(2−y)(PO₄)₃ where 0≦y≦2, M′ and M″ are each metallicelements selected from the group consisting of metal and semi-metalelements, and said M′ and M″ are the same or different from one another:a. where M′ and M″ are the same, they are titanium; and b. where M′ andM″ are different from one another, at least one of M′ and M″ istitanium.
 30. The cell according to claim 29 wherein M′ and M″ aredifferent from one another and they are each independently selected fromthe group of transition metals.
 31. The cell according to claim 29wherein M′ and M″ are different from one another, M′ is a metallicelement which is not a transition metal, and M″ is titanium.
 32. Thecell according to claim 29 wherein said Li₃M′M″(PO₄)₃ is selected fromthe group consisting of Li₃Ti₂ (PO₄)₃, Li₃Ti_(y)V_(2−y)(PO₄)₃,Li₃Ti_(y)Fe_(2−y)(PO₄)₃, Li₃Ti_(y)Cr_(2−y)(PO₄)₃,Li₃Ti_(y)Mn_(2−y)(PO₄)₃, Li₃Ti_(y)MO_(2−y)(PO₄)₃, Li₃Ti_(y)Co_(2−y)(PO₄)₃, Li₃Ti_(y)Al_(2−y)(PO₄)₃, Li₃Ti_(y)Ni_(2−y)(PO₄)₃, and mixturesthereof.
 33. An electrochemical cell which comprises a first electrodeand a second electrode which is a counter electrode to said firstelectrode, said first electrode comprising a lithium-metal-phosphatecompound of the nominal general formula Li₃E′_(y)E″_(2−y)(PO₄)₃ where0≦y≦2, and elements E′ and E″ are the same or different from oneanother: a. where E′ and E″ are the same element, said element istitanium; and b. where E′ and E″ are different from one another, one istitanium.
 34. The cell according to claim 33 wherein at least one ofsaid E′ and E″ is selected from the group of metal and semi-metalelements.
 35. A method for operating an electrochemical cell comprising:a. providing a first electrode composition comprising alithium-metal-phosphate compound, a counter electrode to said firstelectrode, and an electrolyte therebetween; b. electrochemicallyextracting lithium ions from the lithium-metal-phosphate compound andtransferring said ions to the counter electrode to charge said cell; andthen c. electrochemically removing at least a portion of saidtransferred lithium ions from said counter electrode for reinsertioninto said lithium-metal-phosphate compound, whereupon electrochemicalenergy is obtained from the cell during discharge.
 36. The methodaccording to claim 35 wherein said lithium-metal-phosphate compound hasa proportion of 3 lithium ions per formula unit of the metal phosphate;whereupon during extraction the proportion of lithium ions per saidformula unit is less than
 3. 37. The method according to claim 35 where,in step (a), said lithium-metal-phosphate compound is represented by thenominal general formula Li_(3−x)M′_(y)M″_(2−y)(PO₄)₃ where in an initialor uncharged state of said cell, x is 0; and wherein after step (b) andbefore step (c) said lithium-metal-phosphate compound is represented bysaid nominal general formula where x is greater than 0 and less than orequal to 3; and wherein after step (c), steps (b) and (c) are repeatedin sequence.
 38. The method according to claim 35 wherein saidlithium-metal-phosphate is represented by the nominal general formulaLi_(3−x)M′_(y)M″_(2−y)(PO₄)₃ and where during cycling (charge anddischarge) the value of x lithium ions transferred between saidelectrodes varies as 0≦x≦3.
 39. The method according to claim 35 whereinsaid lithium-metal-phosphate is represented by the nominal generalformula Li₃E′_(y)E″_(2−y)(PO₄)₃ wherein said E′ is a transition metalselected from the group consisting of titanium (Ti), vanadium (V),chromium (Cr), manganese (Mn), cobalt (Co), molybdenum (Mo), nickel(Ni), iron (Fe), copper (Cu) and mixtures thereof; said E″ is the sameas or different from E′, and E″ is a metal or semi-metal; and 0≦y≦2. 40.A method for operating an electrochemical cell comprising: a providing afirst electrode composition comprising a lithium-metal-phosphatecompound, a counter electrode which does not contain lithium, and anelectrolyte therebetween; b. electrochemically extracting lithium ionsfrom the lithium-metal-phosphate compound and transferring said ions tothe counter electrode to charge said cell; and then c. electrochemicallyremoving at least a portion of said transferred lithium ions from saidcounter electrode for reinserting into said lithium-metal-phosphatecompound, whereupon electrochemical energy is obtained from the cellduring discharge; and provided that: in step (a), saidlithium-metal-phosphate compound is represented by the nominal formulaLi_(3−x)M′_(y)M″_(2−y)(PO₄)₃, 0≦y≦2, wherein an initial or unchargedstate of said cell, x is 0, M′ and M″ are the same or different and areeach independently selected from the group consisting of metals andsemi-metals; and wherein after step (b) and before step (c) saidlithium-metal-phosphate compound is represented by said nominal formulawhere x is greater than 0 and less than or equal to
 3. 41. The method ofclaim 40 wherein after step (c), steps (b) and (c) are repeated insequence.
 42. The method according to claim 40 , wherein during cycling(charge and discharge) the value of x lithium ions transferred betweensaid electrodes varies as 0≦x≦3.